Thermal insulating material



1941- w. G. STILL 2,261,307

- THERMAL INSULATING MATERIAL Filed Feb. 14, 1939 2 Sheets-Sheet 1 wig/ Ami Nov. 4, 1941. w. G. STILL THERMAL INSULATING MATERIAL 2 Sheets-Sheet 2 Filed Feb. 14, 1939 Patented Nov. 4, 1941 UNITED STATES PATENT OFFICE mmmii'ilmm William George sou, Goodmayes, rim-a, England 3 Application February 14, 1939, Serial No. 256,395 In Great November 8, 1938 The invention consists in improvements in thermal insulating material of the lclnd comprising a pair of reflecting surfaces, frequently composed of metal foil and usually parallel with one another, spaced apart by a separator. Thermal insulating material of this kind is used for the heat insulation of refrigerators and refrigerated chambers as well as for the insulation of heated bodies and other purposes. The invention is particularly concerned with the separator.

Many forms of separator have been proposed for use in thermal insulating material of the above kind and as examples, separators of corrugated sheet material (usually metal foil) have been employed and it has also been suggested to provide separators by pressing up parts of one or both of the reflecting sheets into the form of cups or ribs. It has also been proposed to form a separator by making a succession of zig-zag folds (like a fan) in a length of metal foil, providing slots at the edges of the folds with the slots at one edge staggered in relation to those at the other, and then drawing the folds apart to form a grating whereof the walls will be perpendicular to the general planes of the surfaces which are spaced by the separator.

The object of this invention is to provide thermal insulating material having an improved separator for maintaining the reflecting surfaces at the desired separation and for giving low heat conductivity between the surfaces.

The invention accordingly provides thermal insulating material comprising a pair of substantially parallel reflecting sheets spaced apart by a separator consisting of sheet material .cut and expanded into narrow substantially parallel strips of wavy formation connected by their adjacent edges at intervals along their length and all lying with their width extending obliquely and in the same general direction to the planes of the reflecting sheets spaced by the separator.

Preferably, according to the invention, the

' separator is constructed from a flat sheet of bright metal foil (e. g. aluminum foil) in which substantially parallel rows of slits (or slots) have been made with the slits in each row staggered in overlapping relationship to those in adjacent rows and to which tension has been applied to open up the slits and to turn the material between the rows of slits at an oblique angle (e. g. 45) to the general planes of the spaced reflecting sheets. a

It has been found by experiment that the o about inch and the spacing of the rows of the slits may be such that the overall thickness of the expanded material is about inch or say between $4 and 5 inch. To obtain this result the spacing between the slits which are not staggered in relation to each other, i. e. the spacing between alternate rows of slitamay be about V2 to inch.

The invention includes and for use in the production of thermal insulating material as described above, an element comprising a sheet of bright metal foil and secured to one side of it a sheet of bright metal foil expanded as described.

Some specific embodiments of the thermal insulating material and one practical application of the material will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a plan view of part of a thermal insulating element;

Figure 2 is a section on the line 22 in Figure 1;

Figure 3 is an end view of the element shown in Figure 1;

Figure 4 is a 'sideview of a plurality of elements as shown in Figures 1 to 3 assembled to form the insulating material;

Figure 5 shows a part of a sheet of metal foil slitted ready for expansion;

Figure 6 shows a part of the sheet shown in Figure 5 after expansion;

Figure 7 is a view similar to Figure 3 of a modifled form of insulating element;

Figure 8 is a view similar to Figure 3 of a further modified form of insulating element, and

Figure 9 is a diagram showing the application of the insulating material to a refrigerator.

Like reference numerals designate like parts in the several figures of the drawings.

The element shown in Figures 1 to 3 consists of a sheet I of bright aluminium foil and a separator 2 of expanded bright aluminium foil. The separator is prepared by making rows of slits 3 as shown in Figure 5 in the foil, the slits of each row being staggered in relation to the slits of adjacent rows, but so arranged that the ends of th slits overlap the ends of the slits in adjacent rows. Tension is then applied to the sheet in a direction transverse to the length of the slits to expand the material into the form shown in Figures 1 to 3 in which the strips 4 between the slits are bent to the wavy formation shown and are all turned to lie with their width extimum spacing between the reflecting sheets is tending obliquely and in the same direction to the general plan of the material. The gaps between the ends of the slits form connections between the strips 4 in adjacent rows and in the expanded form of the material the connections between each strip such as the strip I and the strip 1 adjacent to its edge I lying nearer to the reflecting material I are positioned at the tops of the waves in the strip I as shown at 8 and the connections between the strip 5 and the strip 9 adjacent to its edge II lying further from the reflecting material are positioned at th bottoms of the waves in the strip I as shown at II.

The expanded sheet is secured to the reflecting sheet I by simple chain stitching with flexible metal wire I 2 which is preferably covered with cotton, rubber, asbestos or silk such as is used for electrical insulation purposes. Threads of material other than wire may be used for stitching the sheets together and the stitches may be of a form other than the simple chain stitch such as a lock stitch.

.In order to facilitate the manufacture of the elements the reflecting material I and the separator 2 are made in the form of continuous strips which may be joined by their edges to form strips or sheets of any desired width. The strips may be joined by a lap joint as shown at It and for this purpose the edge ll of the separator is set in from the edge I5 of the reflecting strip.

The complete thermal insulating material is prepared from elements as described above by stacking them one on top of the other as shown in Figure 4 and with a flnal cover sheet of aluminium foil.

In order to reduce the risk of tearing the aluminium foil at the ends of the slits when it is being expanded each end of the slits may terminate in a curved or circular hole of small radius as shown at It in Figure 5. When the slits are provided with holes in vthis way the expanded material has the form shown in Figure 6. The provision of holes I 6 is particularly important when the foil is extremely thin.

Figure 7 shows a modified form of the insulating element shown in Figures 1 to 3 in which the edges of the strips 4 are corrugated. These corrugations are produced by using a slitting tool of corresponding shape for the preparation of the slits 3 in the aluminium foil before expansion. In a further alternative form the edges of the strips 1 have, a saw-tooth formation as shown in Figure 8. The formation of the strips with corrugated or saw-toothed edges in this way has the advantage that it provides an effective means of producing point contacts between the expanded sheet and the plane foil which reduces the slit transmitted by conductivity. A further means of ensuring point contact between the reflecting sheet I and the expanded sheet 2 is to corrugate the sheet I as shown in Figure 8. Corrugation of the sheet I in thi way also has the advantage that it tends to diffuse the reflected rays.

The improved thermal insulating material may be used for any of the purposes for which material of this type is commonly employed and Figure 9 shows the application of the material to a domestic refrigerator. In this application of the material a stack II consisting of a plurality of elements as shown in Figures 1 to 3, arranged as shown in Figure 4 is inserted inside a jacket II surrounding the inner lining II of the refrigerator.

I claim:

1. Thermal insulating material comprising two substantially parallel reflecting sheets of bright metal foil spaced apart by a separator consisting of a bright metal foil sheet in expanded, reticulated form, the narrow connective elements thereof being arcuate in shape whereby minimum contact with said spaced sheets is established and the said connective elements being obliquely related to the general plane of the sheets spaced by the separator.

2. Thermal insulating material as claimed in claim 1 in which the edges of the strips of the separator are corrugated.

3. Thermal insulating material as claimed in claim 1 in which the edge of the strips of the separator are of saw-tooth formation.

4. Thermal insulating material as claimed in claim 1 in which the ends of the slits in the separator sheet terminate in round holes.

5. Thermal insulating material as claimed in claim 1 in which the strips of the separator lie with their width at an angle of about to the general planes of the spaced reflecting sheets.

WILLIAM GEORGE STILL. 

